1. Field of the Invention
The present invention relates to a vehicle traction device.
2. Background Art
Usually, when a vehicle, disabled due to a mechanical failure, traffic accident or the like, is towed by a wrecker, its front or rear wheels are kept up while the remaining wheels are left to roll.
FIG. 9 schematically shows how the front wheels of a vehicle 101, disabled due to a mechanical failure, traffic accident or the like, is lifted up when towed. As shown, a T-shaped arm 102 is extended from the wrecker 100 toward the towed vehicle 101. The front wheels are lifted up as a lower portion (front axle some other member in the vicinity thereof) of the towed vehicle 101 is held by vehicle traction attachments 103 fixed on the arm 102.
Loads carried by big-size trucks and other vehicles are recently becoming heavier. This has heightened the necessity to reduce the axle weights which act on tires. Therefore, there is a tendency for big-size vehicles to increase the number of tires per vehicle. In the field of big-size vehicles, four-axle type vehicles are consequently becoming more popular than conventionally dominant three-axle type vehicles such as the one shown in FIG. 9.
FIGS. 10A and 10B are schematic diagrams where a three-axle type big vehicle is compared with a four-axle type big vehicle. FIG. 10A is a side view of the three-axle type big vehicle while FIG. 10B is that of the four-axle type big vehicle. As shown in FIG. 10A, the three-axle type big vehicle has one axle on the front wheel side and two axles on the rear wheel side. In the case of the four-axle type big vehicle shown in FIG. 10B, it has two axles on both front and rear wheel sides. Since the four-axle type big vehicle is thus provided with two axles on the front wheel side, the individual axle weights can be reduced.
As the amount of load carried by a vehicle increases, its center of gravity goes higher. Therefore, the four-axle type big vehicle is provided with smaller-diameter tires than the three-axle type big vehicle. Since this lowers the center of gravity, it is possible to stably drive the vehicle even when the vehicle is fully loaded.
As described above, since the four-axle type big vehicle can lighten the axle weights and lower the center of gravity, it is possible to increase the amount of load carried as compared with the three-axle type big vehicle. It is therefore expected that the demand for four-axle type big vehicles will increase further.
However, since the four-axle type big vehicle employs smaller-diameter tires, its chassis is lower than that of the three-axle type big vehicle. Therefore, as shown in FIG. 10, the front bumper 104 of the four-axle type big vehicle is lower than that of the three-axle type big vehicle as well.
Therefore, the four-axle type big vehicle has a smaller space between the bumper 104 and the ground than that of the three-axle type big vehicle. This poses a problem that the bumper 104 may interfere with the attachments 103 when the attachments 103 are inserted below the chassis of the four-axle type big vehicle in order to tow the vehicle.
If interference occurs between the attachments 103 and the bumper 104, it is not possible to insert the attachments 103 below the chassis. In this case, troublesome operation is required. As shown in FIG. 11, the front wheels of the towed vehicle 101 must be put on a spacer 105 to secure a sufficient space between the bumper 104 and the ground before the attachments 103 are inserted.
In addition, even after the attachments 103 are inserted below the chassis, there remains a problem that since the top surface of the arm 102 is not so distant from the bottom surface of the bumper 104 of the four-axle type big vehicle, the arm 102 may come in contact with the bumper 104 due to vibrations, swings and the like during traction. Consequently, the arm 102 or the bumper 104 may be damaged.